Low cost highly isolated RF coupler

ABSTRACT

Methods of assembling a coupler are provided in which a first printed circuit board is provided, and a second printed circuit board is then surface mounted on the first printed circuit board. The first printed circuit board and the second printed circuit board are then electrically and mechanically connected to provide a coupler having a shielded region defined between the first printed circuit board and the second printed circuit board. The shielded region at least partly surrounds a coupler circuit disposed therein.

BACKGROUND OF THE INVENTION

The present invention generally relates to RF couplers, and moreparticularly relates to highly isolated RF couplers.

Conventional RF couplers that can provide a high degree of isolationtypically include connectorized couplers, couplers within isolatedcompartments, or couplers within multi-layer structures. Such couplerstypically employ of bulky, space consuming shielding such as surfacemounted isolation walls, shielding cans, enclosures or other housingsthat are typically placed over the coupler circuit in order to achieve ahigh degree of isolation. Such couplers are discussed in, for example, acopending U.S. application Ser. No. 10/103,277 entitled “A SYSTEM ANDMETHOD OF PROVIDING HIGHLY ISOLATED RADIO FREQUENCY INTERCONNECTIONS”,which is incorporated by reference in its entirety herein.

In many circumstances, however, it is not possible or desirable to usesuch couplers due to cost, space constraints, or other manufacturingconsiderations such as the significant amount of time required toinstall such couplers.

Accordingly, there is a need for low cost RF couplers that are compactyet highly isolated. Ideally such RF couplers would be easilymanufacturable in that they do not require extensive hand assembly toproduce. It would be highly desirable if such RF couplers were easilyintegrateable with modern manufacturing techniques and would allow forcost efficient manufacturing.

SUMMARY OF THE PREFERRED EMBODIMENTS

An aspect of the present invention provides methods of assembling acoupler. A base printed circuit board is provided. A surface mountprinted circuit board is then mounted on the base printed circuit boardsuch that a shielded region is defined between the base printed circuitboard and the surface mount printed circuit board. The shielded regionat least partly surrounds a coupler circuit disposed therein.

Another aspect of the present invention provides coupler assemblies thatinclude a first printed circuit board, and a second printed circuitboard surface mounted on the first printed circuit board. A shieldedregion is defined between the first printed circuit board and the secondprinted circuit board such that the shielded region at least partlysurrounds a coupler circuit disposed therein.

BRIEF DESCRIPTION OF DRAWINGS

The following discussion may be best understood with reference to thevarious views of the drawings, described in summary below, which form apart of this disclosure.

FIG. 1 illustrates an example of a base PCB structure that can be usedto implement aspects of the present invention.

FIG. 2A illustrates bottom view of an example of a surface mountable PCBstructure that can be used to implement other aspects of the presentinvention.

FIG. 2B illustrates top view of the surface mountable PCB structureshown in FIG.2A.

FIG. 3 is a flow chart illustrating a method of assembling a striplinecoupler structure according to aspects of the present invention.

FIG. 4 illustrates an example of a stripline coupler structure resultingfrom assembly of the base PCB structure shown in FIG. 1 and the surfacemountable PCB structure shown in FIG.2 in which the base PCB structureshown in FIG. 1 is electrically and mechanically connected to thesurface mountable PCB structure according to aspects of the presentinvention.

FIG. 5A illustrates a cross sectional view of the stripline couplerstructure shown in FIG. 4, taken along line SA-5A of FIG. 4.

FIG. 5B illustrates a cross sectional view of the stripline couplerstructure shown in FIG. 4, taken along line 5B-5B of FIG. 4.

FIG. 6 illustrates another example of a base PCB structure that can beused to implement aspects of the present invention.

FIG. 7 illustrates another example of a surface mountable PCB structurethat can be used to implement other aspects of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. In thedrawings, the size of functional units are exaggerated for clarity. Likenumbers refer to like elements throughout.

It will be understood that when an element such as a circuit, structure,region, board or area is referred to as being “connected to” anotherelement, it can be directly connected to the other element orintervening elements may also be present. In contrast, when an elementis referred to as being “directly connected to” another element, thereare no intervening elements present. When an element such as a circuit,structure, region, board or area is referred to as being “adjacent” or“proximate” another element, it can be near the other element but notnecessarily independent of the other element. When an element such as acircuit, structure, region, board or area is referred to as being“between” two things, it can be either partly of completely betweenthose two things, but is not necessarily completely and continuouslybetween those two things. The term “adapted to” should be construed tomean “capable of”.

The term stripline generally denotes a structure comprising a signalconducting strip and two ground planes which extend considerably intransverse directions. The space between the ground planes is filledwith a dielectric medium and the central strip is embedded in thisdielectric. The ground planes are at zero RF potential relative to eachother. Stripline is compatible with automated Surface Mount Technology(SMT) assembly process flows.

By contrast, the term microstrip generally denotes an unshieldedtransmission line comprising a single dielectric substrate with groundplane on one side and a signal conducting strip on the other face.Unlike stripline, SMT components can be attached directly to the signalconducting top layer of microstrip. However, microstrip is alsogenerally subject to Electromagnetic Interference (EMI) from nearbyconductors because of its unshielded structure.

Practice of preferred aspects of the present invention can providecouplers exhibiting a stripline structure yet that can provide thedirectivity offered by microstrip applications.

Aspects of the present invention relate to placement of an RF coupler inan area that requires a high level of isolation at a low cost. Aspectsof the present invention can provide for-a compact RF coupler design,while maintaining the radiated isolation shielding. Aspects of thepresent invention can also provide compact coupler assemblies that takeup less space and that can therefore greatly expand the number and typeof integration options. As a result, the integration density offered bysuch couplers can be vastly increased, thereby allowing for increasedminituraization. Aspects of the present invention can also providecoupler assemblies that can also significantly decrease the cost of thecoupler in comparison to more expensive connectorized couplers and/orcouplers having separate isolation walls soldered to the PCB. Inaddition, manufacture of such coupler assemblies is much easier sinceless labor is involved.

Aspects of the present invention can provide coupler assembliescomprising a first printed circuit board, a second printed circuitboard, and a shielded region. The second printed circuit board can besurface mounted on the first printed circuit board. The shielded regioncan defined between the first printed circuit board and the secondprinted circuit board such that the shielded region at least partlysurrounds a coupler circuit disposed therein.

In some embodiments, the first printed circuit board can a firstetchback area, and the second printed circuit board can include a secondetchback area. The shielded region can then be defined, for example,between the first etchback area and the second etchback area. Thecoupler circuit can then be disposed in at least one of the firstetchback area and the second etchback area. The shielded region ispreferably at least partly filled with a dielectric material.

The coupler circuit may include, for example, a first RF structure, asecond RF structure, and a transition region. The second RF structure iscoupled to the first RF structure. The first RF structure can bedisposed on at least one of the first printed circuit board and thesecond printed circuit board. The second RF structure can be disposedproximate the first RF structure on at least one of the first printedcircuit board and the second printed circuit board. The second RFstructure is disposed proximate the first RF structure to provide afixed coupling ratio between the first RF structure and the second RFstructure. The transition region can also be disposed on at least one ofthe first printed circuit board and the second printed circuit board.

In some embodiments, the first RF structure that can be matched to themicrostrip transition areas, and is disposed in a second etchback area.The second RF structure can then be disposed proximate the first RFstructure. In other embodiments, a stripline structure is used in whichthe first RF structure is continuous with microstrip transition areas.In this case, the first printed circuit board further comprises a secondRF structure disposed proximate the first RF structure.

In still other embodiments, the second printed circuit board can includea first side contacting the first printed circuit board, a second sidecomprising a ground plane, and means for connecting disposed on thesecond side. The first printed circuit board can include a first sidefor contacting the first side of the second printed circuit board. Thefirst side can comprise a ground plane, a plurality of microstriptransition areas, and the first etchback area.

Aspects of the present invention can also provide methods of assemblingcouplers in which a first printed circuit board can be provided, andthen a second printed circuit board is surface mounted on the firstprinted circuit board to define a shielded region between the firstprinted circuit board and the second printed circuit board. The shieldedregion at least partly surrounds a coupler circuit disposed therein. Asolder re-flow operation can then be performed to electrically andmechanically connect the first printed circuit board to the secondprinted circuit board to thereby provide a stripline structure.

Coupler assemblies according to aspects of the invention will now bediscussed with reference to a base PCB such as that shown in FIG. 1 anda surface mountable PCB structure such as that shown in FIG. 2A and 2B.It will be appreciated that coupler assemblies according to aspects ofthe invention are not limited to the embodiments shown in the drawings.

As shown in FIG. 4, the coupler assembly 300 can include a base printedcircuit board 100 upon which a surface mount printed circuit board 200is mounted and subsequently connected.

FIG. 1 illustrates an example of a base printed circuit board (PCB)structure 100 that can be used to implement aspects of the presentinvention.

When a single layer PCB is used for the base printed circuit board 100,the base printed circuit board 100 can include an insulator layer 115and a patterned conductive layer 120 that is grounded. However, itshould be appreciated that the base printed circuit board 100 cancomprise either a single layer printed circuit board or a multiple layerprinted circuit board.

The base printed circuit board 100 can include RF circuitry on the board100. Other possible circuitry can include all printable topologies andcomponents held only to the bounds of the physical property of thematerials. For example, filters (planar and photonic band gap),detectors (all types), attenuators, and/or isolated “through wall” RFoutput (see copending U.S. application Ser. No. 10/103,277 entitled “ASYSTEM AND METHOD OF PROVIDING HIGHLY ISOLATED RADIO FREQUENCYINTERCONNECTIONS”, which is incorporated by reference in its entiretyherein).

The patterned conductive layer 120 is provided on a first face of theinsulator layer 115. The patterned conductive layer 120 defines anetchback or gap region 190 therein that exposes a portion of theinsulator layer 115. In a single layer configuration, the base printedcircuit board 100 can include a dielectric layer 115 disposed betweenthe first face 125 contacting the surface mount printed circuit board200, and a second face 110 of the base printed circuit board 100.

Microstrip transition areas 140 can also be located on the first face125. The microstrip transition areas 140 are preferably disposed in thefirst etchback area 190 for coupling to a main RF thru structure 240.The second face also includes a ground plane 110 that is coupled to thepatterned conductive layer 120, for example, by wrapping around edgeportions of base PCB 100.

The base PCB 100 can also include features required to accomodate matingcomponents such as a clearance 150 adapted to accomodate a terminationresistance 250, a clearance 160 adapted to accomodate a coupled portconnector 280, and a plurality of connection points 170 provided in theconductive layer 120. The connection points 170 are sometimes referredto as “vias.” The connection points or vias 170 can be disposed adjacentthe etchback region 190. The connection points or vias 170 are disposedbetween the ground plane 110 and the patterned conductive layer 120,thus maintaining substantially equal electrical potential on bothsurfaces.

FIG. 2A illustrates bottom view of a surface mountable PCB 200 structurethat can be used to implement other aspects of the present invention.When a single layer PCB is used, an insulator layer 215 is interposedbetween a patterned conductive layer 220 and a ground plane conductorlayer 210. The insulator layer is typically a layer of dielectricmaterial 215 interposed between a first ground plane 225 and a secondground conductor layer 210. The first ground plane 225 is typicallycoupled to the second ground conductor layer 210 via edge plating (notshown), plated throughholes (not shown) and the like.

The first face of the first ground plane 225 can include, for example,conductive tab regions 220, 270, a main RF thru structure 240, and acoupled RF structure 260. The conductive tab regions 220, 270 define asecond etchback area 290 on a lower face or side of the surface mountprinted circuit board 200. In the embodiment shown in FIG. 2A, the mainRF thru structure 240 is disposed in the second etchback area 290. Themain RF thru structure 240 is preferably matched for coupling to themicrostrip transition areas 140. In other words, the main RF thrustructure 240 is preferably constructed to have a strip width that willyield a desired characteristic impedance when separated from a groundplane by a dielectric sheet of a given thickness. Upon assembly,constructing the main RF thru structure 240 and the microstriptransition areas 140 in this manner will allow for a matched microstriptransmission line to be provided. To achieve matching, the width of themicrostrip transition areas 140 may change as they pass under thesurface mountable PCB 200 structure so that the width matches that ofthe main RF thru structure 240.

As noted above, the coupled RF structure 260 can also be disposed in thesecond etchback area 290 proximate the main RF thru structure 240. Thecoupled RF structure 260 is connected to the coupled port connector 280.The coupled radio frequency structure 260 can include, for example, atermination resistance 250.

FIG. 2B illustrates top view of the surface mountable PCB structureshown in FIG. 2A. As shown in FIG. 2B, a launch or coupled portconnector 280 is provided to allow for connection to another circuitsuch as a power amplifier. The coupled port connector 280 can bedisposed on the second face of the ground plane conductor layer 210. ThePCB 200 can also provide features required for mating to the base PCB100, such as connectivity points 270.

In the embodiment shown in FIG. 2B, the surface mount printed circuitboard 200 includes a main RF thru structure 240 coupled to themicrostrip transition areas 140. The surface mount printed circuit board200 also includes a coupled RF structure 260. The coupled RF structureis disposed proximate a main RF thru structure 240 such that a fixedcoupling ratio is provided between the main RF thru structure 240 andthe coupled RF structure 260. It should be appreciated that the main RFthru structure 240 and the coupled RF structure 260 could likewise bedisposed on the base printed circuit board 100, as shown in FIGS. 6 and7.

Thus, the surface mounted PCB 200 of the embodiment shown in FIG. 2Bincludes the coupler circuit structure 240, 260 including a terminationport resistance 250, coupled port connector 280, and appropriategrounding 220 with connectivity points 270.

FIG. 3 is a flow chart illustrating a method of assembling a striplinecoupler structure according to aspects of the present invention.

At step 310, a base printed circuit board 100 such as that discussedabove is provided. The base printed circuit board includes conductiveregions 120 that define a first etchback area 190 in which a pluralityof microstrip transition areas 140 are provided.

At step 320, the surface mount printed circuit board 200 is mounted onthe base printed circuit board 100 using conventional surface mounttechnology (SMT). The base printed circuit board 100 includes an outline130 that serves as a target for placement of the first face 225 of thesurface mount printed circuit board 200. The base printed circuit board100 can also include a clearance 150 for accommodating the terminationresistor 250, and a clearance 160 for accomodating the coupled portconnector 280. The surface mount printed circuit board 200 also includesthe second etch back area 290.

At step 330, a solder re-flow operation is performed that connects thebase printed circuit board 100 to the surface mount printed circuitboard 200. At least some of the plurality of connection points 170 areused during the solder reflow to establish a connection with theplurality of connection points 270 from through the surface mountableprinted circuit board 200. As a result, during the solder reflowoperation the two PCBs are electrically and mechanically connected,creating a stripline structure, as shown in FIG. 4.

FIG. 4 illustrates an example of the completed stripline couplerstructure resulting from assembly of the base PCB structure shown inFIG. 1 and the surface mountable PCB structure shown in FIGS. 2A and 2Bin which the base PCB structure shown in FIG. 1 is electrically andmechanically connected to the surface mountable PCB structure accordingto aspects of the present invention.

FIG. 5A illustrates a cross sectional view of the stripline couplerstructure shown in FIG. 4, taken along line 5A-5A of FIG. 4. FIG. 5Billustrates a cross sectional view of the stripline coupler structureshown in FIG. 4, taken along line 5B-5B of FIG. 4. Once assembled, themain RF thru structure 240 becomes a stripline conductor, and thecoupler takes on a surface mount “stripline board” type structure. Asnoted above, those skilled in the art will realize that a striptransmission line is a conductor disposed between two ground planes,while a microstrip line is a conductor disposed above a single groundplane. Joining the main RF thru structure 240 to the microstriptransition areas 140 can provide the coupler circuit structure 240, 260including a termination port resistance 250 and coupled port connector280. A coupled RF structure 260 disposed proximate the main RF thrustructure 240 can provide a coupler circuit having a fixed couplingratio. The shielded region 400 between the surface mount printed circuitboard 200 and the base printed circuit board 100 can be filled with airor other known dielectric materials.

In the completed coupler 300, the ground plane 120 of the base circuitboard 100 and conductive tab regions 220 are electrically andmechanically connected. In turn, the ground plane 120 is electricallyconnected to the ground plane 210 of the surface mount circuit board200. In the embodiment shown in FIG. 4, the ground planes 120, 210 areinterconnected using connection points 170, 270. Such interconnectionscan be accomplished, for example, by using conductive through-holes suchas those shown in FIGS. 5A and 5B.

By electrically and mechanically connecting the ground planes 120, 210of the PCBs in a manner such that they surround the coupler circuit, acoupler circuit 240, 260 having a highly isolated stripline structure isprovided within a shielded region 400 defined between the first etchbackarea 190 and the second etchback area 290. As noted above, the shieldedregion 400 is filled with insulative material 410 that comprises adielectric such as glass teflon, glass epoxy, ceramic and the like.Alternative embodiments include dielectrics that are suitable for theconstruction of flexible PCBs.

Bringing a controlled impedance transmission line such as a striplinetransmission line, through the shielded region can result in minimaldisruption in its impedance. The shielded region 400 can thus serve toshield the coupler circuit, formed from the main RF thru structure 240and the coupled RF structure 260, and thereby prevent the circuit fromabsorbing electromagnetic energy. Electromagnetic energy may be in theform of electromagnetic radiation that is typically impinging on the PCB100, or that is generated by circuitry (not shown) disposed on PCB 100.The shielded region 400 can also prevent the coupler circuit fromemitting electromagnetic energy.

As a result, compact, surface mount couplers can be provided that canprovide a high degree of isolation. Such couplers are less costly thanconventional “off-the-shelf” connectorized couplers and couplersimplementing separate isolation walls soldered to the PCB. Such couplerscan also provide a much more compact design in comparison to other RFcouplers. In turn, possible integration options are greatly increased.

By replacing the PCB shown in FIG. 2A, the RF performance can beflexibly controlled based on the requirements of the user. Accordingly,such manufacturing flexibility can allow coupler values and frequenciesto be optimized in situations in which couplers were mutually exclusive.This in turn can also allow for “PCB sharing.”

The aspects of the present invention described above can have manypractical variations. With the growing need of derivative products thisdesign can be quickly conformed both in higher frequencies and couplingvalues. This can allow the coupler assemblies described above to bequickly conformed to higher frequencies. Moreover, this can also allowthe coupler assemblies described above to be quickly conformed to othercoupling values.

While aspects of the present invention have been described in terms ofcertain preferred embodiments, those of ordinary skill in the willappreciate that certain variations, extensions and modifications may bemade without varying from the basic teachings of the present invention.For example, coupler assemblies according to aspects of the inventioncan utilize a base PCB such as that shown in FIG. 1 and a surfacemountable PCB structure such as that shown in FIGS. 2A and 2B. It shouldbe appreciated that while certain embodiments of the coupler assembliescan utilize a base PCB such as that shown in FIG. 1 and a surfacemountable PCB structure such as that shown in FIG. 2B, the presentinvention is not limited to these particular embodiments. For example,FIG. 6 illustrates one example of alternative structures to the base PCBshown in FIG. 1 and FIG. 7 illustrates one example of alternativestructures to the surface mountable PCB structure shown in FIG. 2,respectively. In such embodiments, the base printed circuit board 100can include a main RF thru structure 240, and a coupled RF structure260. The main RF thru structure 240 can disposed in the first etchbackarea 190. In this case, the main RF thru structure 240 is continuouswith or part of the microstrip transition areas 140. The coupled RFstructure 260 can also be disposed in the first etchback area 190proximate the main RF thru structure 240. Thus, as shown in FIGS. 6 and7, it will be appreciated that the main RF thru structure 240 andmicrostrip transition areas 140 could initially be provided in the firstetchback area 190 and subsequently connected to a termination resistance250 and annular ring structure 310 provided in the second etchback area290.

Aspects of the present invention can be implemented, for example, onsingle layer printed circuit boards (PCBs) that can benefit from highisolation that stripline structures typically afford. Specializedcircuit functions including RF power amplifiers are conventionallyfabricated on PCB materials, including hard or brittle ceramicsubstrates, that are not compatible with multilayer PCB fabricationtechniques. In the past, the inclusion of stripline as an inherent partof the unpopulated PCB has not been possible. In addition, single layerprinted circuit boards (PCBs) may be useful where a connectorizedcoupler might not fit and/or needs to be removed. It should beappreciated that, the base PCB discussed herein could be either a singlelayer printed circuit board or a multiple layer printed circuit board.

As such, aspects of the present invention are not to be limited to thespecific preferred embodiments described herein. Rather, the scope ofthe present invention is to be determined from the claims, which follow.

1. A coupler assembly, comprising: a first printed circuit board; and asecond printed circuit board surface mounted on the first printedcircuit board; and a shielded region defined between the first printedcircuit board and the second printed circuit board, wherein the shieldedregion at least partly surrounds a coupler circuit disposed therein. 2.A coupler assembly according to claim 1, wherein the first printedcircuit board includes a first etchback area, the second printed circuitboard includes a second etchback area, the shielded region is definedbetween the first etchback area and the second etchback area, and theshielded region at least partly surrounds a coupler circuit disposed inat least one of the first etchback area and the second etchback area. 3.A coupler assembly according to claim 2, wherein the coupler circuitcomprises: a first RF structure on at least one of the first printedcircuit board and the second printed circuit board; a second RFstructure disposed proximate the first RF structure on at least one ofthe first printed circuit board and the second printed circuit board,wherein the second RF structure is coupled to the first RF structure;and a transition region on at least one of the first printed circuitboard and the second printed circuit board.
 4. A coupler assemblyaccording to claim 2, wherein the second printed circuit board includes:the first RF structure disposed in a second etchback area, wherein thefirst RF structure is matched to microstrip transition areas, a secondRF structure disposed proximate the first RF structure.
 5. A couplerassembly according to claim 2, wherein the first RF structure iscontinuous with microstrip transition areas, wherein the first printedcircuit board further comprises: a second RF structure disposedproximate the first RF structure.
 6. A coupler assembly according toclaim 1, wherein the second RF structure is disposed proximate the firstRF structure such that the first RF structure and the second RFstructure maintain a fixed coupling ratio therebetween.
 7. A couplerassembly according to claim 1, wherein the shielded region is at leastpartly filled with a dielectric material.
 8. A coupler assemblyaccording to claim 1, wherein the second printed circuit board includes:a first side contacting the first printed circuit board; a second sidecomprising a ground plane; and means for connecting disposed on thesecond side.
 9. A coupler assembly according to claim 1, wherein thefirst printed circuit board includes a first side contacting the firstside of the second printed circuit board, wherein the first sidecomprises a ground plane, a plurality of microstrip transition areas,and the first etchback area.
 10. A coupler assembly, comprising: a firstprinted circuit board including a plurality of microstrip transitionareas disposed in a first etchback area; and a second printed circuitboard having a second etchback area, and coupled to the first printedcircuit board; wherein at least one of the first printed circuit boardand the second printed circuit board includes: a first RF structurecoupled to the microstrip transition areas, a second RF structuredisposed proximate the first RF structure, wherein a shielded region isdefined between the first etchback area and the second etchback area.11. A coupler assembly according to claim 10, wherein the second printedcircuit board includes: a first RF structure disposed in a secondetchback area, wherein the first RF structure is matched to themicrostrip transition areas, a second RF structure disposed proximatethe first RF structure.
 12. A coupler assembly according to claim 10,wherein the first RF structure is continuous with the microstriptransition areas, wherein the first printed circuit board furthercomprises: a second RF structure disposed proximate the first RFstructure.
 13. A coupler assembly according to claim 10, wherein thesecond RF structure is disposed proximate the first RF structure suchthat the first RF structure and the second RF structure maintain a fixedcoupling ratio therebetween.
 14. A coupler assembly according to claim10, wherein the shielded region is filled with a dielectric material.15. A coupler assembly according to claim 10, wherein the second printedcircuit board includes: a first side contacting the first printedcircuit board; a second side comprising a ground plane; and means forconnecting disposed on the second side.
 16. A coupler assembly accordingto claim 10, wherein the first printed circuit board includes a firstside contacting the first side of the second printed circuit board,wherein the first side comprises a ground plane, the plurality ofmicrostrip transition areas, and the first etchback area.
 17. A couplerassembly, comprising: a base printed circuit board including conductiveregions that define a first etchback area, wherein a plurality ofmicrostrip transition areas are disposed in the first etchback area; anda surface mount printed circuit board having a second etch back areacoupled to the base printed circuit board, wherein at least one of thebase printed circuit board and the surface mount printed circuit boardincludes: a main RF thru structure coupled to the microstrip transitionareas; and a coupled RF structure disposed proximate the main RF thrustructure such that a fixed coupling ratio is provided between the mainRF thru structure and the coupled RF structure.
 18. A coupler assemblyaccording to claim 17, wherein the surface mount printed circuit boardincludes: conductive tab regions defining a second etchback area on alower face of the surface mount printed circuit board; a main RF thrustructure disposed in the second etchback area, wherein the main RF thrustructure is matched to the microstrip transition areas; and a coupledRF structure disposed in the second etchback area proximate the main RFthru structure.
 19. A coupler assembly according to claim 17, whereinthe base printed circuit board includes: a main RF thru structuredisposed in the first etchback area, wherein the main RF thru structureis continuous with the microstrip transition areas; and a coupled RFstructure disposed in the first etchback area proximate the main RF thrustructure.
 20. A coupler assembly according to claim 17, wherein ashielded region is defined between the first etchback area and thesecond etchback area.
 21. A coupler assembly according to claim 17,wherein the shielded region is filled with insulative material.
 22. Acoupler assembly according to claim 17, wherein the surface mountprinted circuit board includes: a first face contacting the base printedcircuit board; a second face comprising a ground plane; and means forconnecting disposed on the second face.
 23. A coupler assembly accordingto claim 17, wherein the base printed circuit board includes a firstface contacting the first face of the surface mount printed circuitboard, wherein the first face comprises a ground plane, the plurality ofmicrostrip transition areas, and the first etchback area.
 24. A couplerassembly according to claim 17, wherein the base printed circuit boardincludes RF circuitry thereon.
 25. A coupler assembly according to claim17, wherein the base printed circuit board comprises a single layerprinted circuit board.
 26. A coupler assembly according to claim 17,wherein the base printed circuit board comprises a multiple layerprinted circuit board.
 27. A method of assembling a coupler, comprising:providing a base printed circuit board; and mounting a surface mountprinted circuit board on the base printed circuit board such that ashielded region is defined between the base printed circuit board andthe surface mount printed circuit board, wherein the shielded region atleast partly surrounds a coupler circuit disposed therein.
 28. A methodof assembling a coupler according to claim 27, further comprising:performing a solder re-flow operation that electrically and mechanicallyconnects the base printed circuit board to the surface mount printedcircuit board to thereby provide a stripline structure.
 29. A method ofassembling a coupler according to claim 27, wherein the base printedcircuit board includes a first etchback area, and the surface mountprinted circuit board includes a second etchback area,
 30. A method ofassembling a coupler according to claim 29, wherein the shielded regionis defined between the first etchback area and the second etchback area,such that the shielded region at least partly surrounds a couplercircuit disposed in at least one of the first etchback area and thesecond etchback area.
 31. A method of assembling a coupler according toclaim 27, wherein the coupler circuit comprises: a first RF structure onat least one of the base printed circuit board and the surface mountprinted circuit board; a second RF structure disposed proximate thefirst RF structure on at least one of the base printed circuit board andthe surface mount printed circuit board, wherein the second RF structureis coupled to the first RF structure; and a transition region on atleast one of the base printed circuit board and the surface mountprinted circuit board.
 32. A method of assembling a coupler according toclaim 29, wherein the surface mount printed circuit board includes: thefirst RF structure disposed in a second etchback area, wherein the firstRF structure is matched to microstrip transition areas, a second RFstructure disposed proximate the first RF structure.
 33. A method ofassembling a coupler according to claim 29, wherein the first RFstructure is continuous with microstrip transition areas, wherein thebase printed circuit board further comprises: a second RF structuredisposed proximate the first RF structure.
 34. A method of making acoupler, comprising: providing a first printed circuit board; andsurface mounting a second printed circuit board on the first printedcircuit board; such that a shielded region is defined between the firstprinted circuit board and the second printed circuit board, wherein theshielded region at least partly surrounds a coupler circuit disposedtherein.
 35. A method of making a coupler according to claim 34, furthercomprising: performing a solder re-flow operation that electrically andmechanically connects the first printed circuit board to the secondprinted circuit board to thereby provide a stripline structure.
 36. Amethod of making a coupler according to claim 34, wherein the firstprinted circuit board includes a first etchback area, and the secondprinted circuit board includes a second etchback area, wherein theshielded region is defined between the first etchback area and thesecond etchback area, and wherein the shielded region at least partlysurrounds a coupler circuit disposed in at least one of the firstetchback area and the second etchback area.
 37. A method of making acoupler according to claim 35, wherein the coupler circuit comprises: afirst RF structure on at least one of the first printed circuit boardand the second printed circuit board; a second RF structure disposedproximate the first RF structure on at least one of the first printedcircuit board and the second printed circuit board, wherein the secondRF structure is coupled to the first RF structure; and a transitionregion on at least one of the first printed circuit board and the secondprinted circuit board.
 38. A method of making a coupler according toclaim 35, wherein the second printed circuit board includes: the firstRF structure disposed in a second etchback area, wherein the first RFstructure is matched to microstrip transition areas, a second RFstructure disposed proximate the first RF structure.
 39. A method ofmaking a coupler according to claim 35, wherein the first RF structureis continuous with microstrip transition areas, wherein the firstprinted circuit board further comprises: a second RF structure disposedproximate the first RF structure.
 40. A method of making a coupleraccording to claim 34, wherein the second RF structure is disposedproximate the first RF structure such that the first RF structure andthe second RF structure maintain a fixed coupling ratio therebetween.41. A method of making a coupler according to claim 34, wherein theshielded region is at least partly filled with a dielectric material.42. A method of making a coupler according to claim 34, wherein thesecond printed circuit board includes: a first side contacting the firstprinted circuit board; a second side comprising a ground plane; andmeans for connecting disposed on the second side.
 43. A method of makinga coupler according to claim 34, wherein the first printed circuit boardincludes a first side contacting the first side of the second printedcircuit board, wherein the first side comprises a ground plane, aplurality of microstrip transition areas, and the first etchback area.44. A method of making a coupler, comprising: providing a first printedcircuit board including a plurality of microstrip transition areasdisposed in a first etchback area; and surface mounting a second printedcircuit board having a second etchback area on the first printed circuitboard, wherein at least one of the first printed circuit board and thesecond printed circuit board includes: a first RF structure coupled tothe microstrip transition areas, a second RF structure disposedproximate the first RF structure, and wherein a shielded region isdefined between the first etchback area and the second etchback area.45. A method of making a coupler according to claim 44, furthercomprising: performing a solder re-flow operation that electrically andmechanically connects the first printed circuit board to the secondprinted circuit board to thereby provide a stripline structure.
 46. Amethod of making a coupler according to claim 44, wherein the secondprinted circuit board includes: a first RF structure disposed in asecond etchback area, wherein the first RF structure is matched to themicrostrip transition areas, a second RF structure disposed proximatethe first RF structure.
 47. A method of making a coupler according toclaim 44, wherein the first RF structure is continuous with themicrostrip transition areas, wherein the first printed circuit boardfurther comprises: a second RF structure disposed proximate the first RFstructure.
 48. A method of making a coupler according to claim 44,wherein the second RF structure is disposed proximate the first RFstructure such that the first RF structure and the second RF structuremaintain a fixed coupling ratio therebetween.
 49. A method of making acoupler according to claim 44, wherein the shielded region is filledwith a dielectric material.
 50. A method of making a coupler accordingto claim 44, wherein the second printed circuit board includes: a firstside contacting the first printed circuit board; a second sidecomprising a ground plane; and means for connecting disposed on thesecond side.
 51. A method of making a coupler according to claim 44,wherein the first printed circuit board includes a first side contactingthe first side of the second printed circuit board, wherein the firstside comprises a ground plane, the plurality of microstrip transitionareas, and the first etchback area.
 52. A method of making a coupler,comprising: providing a base printed circuit board including conductiveregions that define a first etchback area, wherein a plurality ofmicrostrip transition areas are disposed in the first etchback area; andsurface mounting a surface mount printed circuit board on the baseprinted circuit board, wherein the surface mount printed circuit boardincludes a second etch back area, wherein at least one of the baseprinted circuit board and the surface mount printed circuit boardincludes: a main RF thru structure coupled to the microstrip transitionareas; and a coupled RF structure disposed proximate the main RF thrustructure such that a fixed coupling ratio is provided between the mainRF thru structure and the coupled RF structure.
 53. A method of making acoupler according to claim 52, further comprising: performing a solderre-flow operation that electrically and mechanically connects the baseprinted circuit board to the surface mount printed circuit board tothereby provide a stripline structure.
 54. A method of making a coupleraccording to claim 52, wherein the surface mount printed circuit boardincludes: conductive tab regions defining a second etchback area on alower face of the surface mount printed circuit board; a main RF thrustructure disposed in the second etchback area, wherein the main RF thrustructure is matched to the microstrip transition areas; and a coupledRF structure disposed in the second etchback area proximate the main RFthru structure.
 55. A method of making a coupler according to claim 52,wherein the base printed circuit board includes: a main RF thrustructure disposed in the first etchback area, wherein the main RF thrustructure is continuous with the microstrip transition areas; and acoupled RF structure disposed in the first etchback area proximate themain RF thru structure.
 56. A method of making a coupler according toclaim 52, wherein a shielded region is defined between the firstetchback area and the second etchback area.
 57. A method of making acoupler according to claim 52, wherein the shielded region is filledwith insulative material.
 58. A method of making a coupler according toclaim 52, wherein the surface mount printed circuit board includes: afirst face contacting the base printed circuit board; a second facecomprising a ground plane; and means for connecting disposed on thesecond face.
 59. A method of making a coupler according to claim 52,wherein the base printed circuit board includes a first face contactingthe first face of the surface mount printed circuit board, wherein thefirst face comprises a ground plane, the plurality of microstriptransition areas, and the first etchback area.
 60. A method of making acoupler according to claim 52, wherein the base printed circuit boardincludes RF circuitry thereon.
 61. A method of making a coupleraccording to claim 52, wherein the base printed circuit board comprisesa single layer printed circuit board.
 62. A method of making a coupleraccording to claim 52, wherein the base printed circuit board comprisesa multiple layer printed circuit board.